(Revised Abstract) DESCRIPTION (provided by applicant): The mission of the Experimental Radiation Shared Service (ERSS) is to provide easy access at a reasonable cost to ionizing radiation for experimental purposes. In order to provide such access, the facility provides necessary training and certification to new users, as well as consultative technical expertise as required. The Experimental Radiation Shared Service at the Arizona Cancer Center (AZCC) consists of a Cobalt-60 teletherapy unit located in a shielded room (0921A) in the basement of the Levy Building, one of the two buildings that comprise the AZCC, and the personnel necessary to support its continued operation and maintenance. This service provides AZCC members with access to a high dose rate ionizing radiation facility dedicated to research; it is the only experimental radiation facility available on the Arizona Health Sciences Center campus. It serves AZCC members and the University of Arizona research community at large, fostering collaborations between the two groups. Currently, the ERSS supports hypothesis-driven, cutting-edge research into the mechanisms involved in radiation response and the development of radiation resistance. It provides a means for testing potential new radiation-sensitizing/protecting drugs and novel methods of radiation-triggered drug delivery. It is furthermore critical to the work of the immunotherapy research program. As long as ionizing radiation is a key component in cancer therapy, the resources of the ERSS will remain critical to Cancer Center members and their research programs.